1. Field of the Invention
The present invention relates generally to an apparatus for handling fabric pieces for apparel manufacture and, in particular, to a novel fabric pickup device for such an apparatus.
2. Description of the Prior Art
In order for a fabric piece handling system to be practical, it must have a high degree of reliability in separating a single piece of fabric from the top of a stack of fabric pieces without picking up two or more pieces. For example, it has been estimated that one malfunction in one thousand operation cycles is the degree of reliability necessary for a profitable manufacturing operation.
U.S. Pat. No. 4,444,384, issued to Keeton, discloses a cloth pickup device including first and second jaws pivotally mounted for movement from a clamping position to an open position. When the jaws are moved into contact with a piece of cloth, they are pivoted to clamp the cloth between them with needles extending from the first jaw piercing the cloth. An overcenter spring holds the jaws in both their first and second positions. When it is desired to release the cloth held by the jaws, a plunger is depressed, engaging the jaws and pivoting them to their open position.
U.S. Pat. No. 4,526,363, issued to Fort, discloses a gripper for textile machines which includes a gripping clamp and an apparatus for opening and closing the clamp. The clamp includes a fixed central member provided laterally and on either side with a resilient portion, two arms crossing each other for constituting a pair of gripping jaws, each arm being provided with a key preferably in the outer extension of the resilient portion. The opening and closing apparatus includes a pair of vertically movable fingers, by reason of one per arm, which are adapted in their lower position to depress the keys in order to cause the distortion of the resilient portions and thus modify the degree of crossing of the jaw forming portions. The height of the vertically movable fingers appears to be adjustable to control the degree of opening of the jaws.
A somewhat similar device is shown in U.S. Pat. No. 4,697,837, also issued to Fort, for a gripper. The gripper includes tongs formed by two oscillating jaws. The jaws are solid in rotation with two shafts rotating in bearings carried by a frame solid with the rod of a jack. The rotation of the shaft is caused by the angular movement of a maneuvering part connecting each shaft to a stationary part.
In addition to the above "pinch-type" devices, various other pickup devices employing one or more gripping clutches have been proposed. U.S. Pat. Nos. 5,018,715 and 3,588,091 and the Tex-Matic product brochure are illustrative of such approaches.
U.S. Pat. No. 5,018,715, issued to Reeves et al., discloses a fabric pickup device useful for a fabric handling system. The fabric pickup device includes a fluid operated cylinder and piston having four individual fabric clutches attached to the cylinder and aligned with and substantially equality spaced apart from the axis of the piston. Each clutch has a head portion having a plurality of resilient pickup fingers spaced apart from one another. A substantially flat actuator plate is attached to the free end of the piston and is oriented perpendicular to the axis of the piston. The actuator plate has a series of apertures for receiving the individual pickup fingers. The openings in the actuator plate are sized such that when the plate is retracted by the action of the fluid cylinder, the resilient fingers of each pickup finger separate and, when the plate is extended, the fingers are brought together to grip the top surface of a fabric piece. Because the pickup fingers are actuated by the movement and contact with the actuator plate and are themselves fixedly mounted to the actuator plate, the vertical position of the pickup fingers remains constant even during actuation, thereby reducing the degree of control necessary for reliable ply separation of small fabric pieces.
U.S. Pat. No. 3,558,091 issued to Stone et al., discloses an apparatus and method for picking up individual pieces of cloth from a stack, carrying the individual pieces of cloth away from the point of picking them up, and depositing them individually on a support, such as a conveyor. The pickup head, as taught by Stone, has a sleeve having one end secured to the piston of an air cylinder and the lower end formed to provide a plurality of equally spaced fingers having cloth-gripping or pinching bottom terminals. The sleeve is surrounded by a head or housing having a bore for receiving the sleeve which includes a lower adjustable portion which has a bore which engages the finger terminals when the air cylinder is actuated. Consequently, when the air cylinder is displaced downwardly, the surfaces of the gripping fingers contact the surface of the lower housing which results in closing the fingers so as to pinch a layer of cloth preparatory to lifting the cloth from the stack.
The Tex-Matic product brochure shows a fabric pickup having six individual gripping fingers equally spaced apart from one another. The fabric pickup device as disclosed by the Tex-Matic product brochure is air operated by a single cylinder which actuates the plurality of pickup fingers simultaneously.
Certain disadvantages become apparent with such designs. First, many of the prior art devices require that the surface of the cloth be penetrated in part by a wire or needle, for example in the construction of the pickup devices as taught by Keeton and Fort '363, in order to increase the reliability of the cloth pickup. Such penetration can result in the introduction of undesirable surface defects, particularly in tightly woven or shear fabrics.
Second, prior art devices have not provided a means for aiding the release of the fabric piece from the pickup device to prevent "sticking" of the fabric piece in the pickup head.
Finally, many prior art pickup devices are designed in such a way that a compound movement in both the vertical as well as the horizontal planes must be made in order to contact and pickup the fabric piece. This requires that the position of the device be carefully controlled in both the x,y directions and the z direction. For example, in the construction of the pickup device as taught by Stone, the pickup fingers themselves actually move downwardly and, consequently, the distance between a fabric piece and the pickup head varies when the device is actuated. As a result, such a device cannot be readily adapted to a simple x,y coordinate control system.
It has thus become desirable to develop a fabric pickup device for a fabric handling apparatus that will reliably pickup and release pieces of fabric from a supported stack of fabric one at a time without picking up two or more pieces. It has also become desirable to develop a pickup device which will not mar the surface of the fabric.